Every year, construction crews across the world strike buried utilities they were not expecting. Gas mains rupture. Fiber-optic cables are severed. Water mains flood active excavations. The financial toll on the global construction industry runs into the billions of dollars annually, and the human toll – injuries, fatalities, service outages affecting hospitals and emergency services – is harder to quantify but no less real.[1]
The troubling pattern in almost every post-incident review is the same: the project had some utility information. There were drawings. There were records. Someone had called in a locate request. The problem was not a complete absence of data – it was an unquantified gap between what was known and what was actually in the ground. That gap is precisely what Subsurface Utility Engineering (SUE) was designed to close, and the ASCE 38 standard provides the formal framework for communicating how wide that gap is on any given project.[2]
ASCE 38-22, the current edition of the standard (originally published as ASCE 38-02), establishes four quality levels – designated D, C, B, and A – that describe with precision what has been confirmed about subsurface utilities at a given location. Understanding what each level actually means, what it confirms, and what it deliberately does not claim is the practical foundation of risk-informed project planning for any engineer, project manager, or infrastructure owner working near buried assets.
๐ Key Points
- ASCE 38-22 defines four SUE quality levels: D (record research), C (surface geophysics – horizontal trace), B (designating – horizontal position confirmed in field), and A (locating – depth and condition by vacuum excavation).
- Quality Level D is the starting point on most projects; Quality Level A is the only level that confirms depth.
- The quality level framework is not a hierarchy of effort – it is a hierarchy of certainty. Each level makes specific, bounded claims.
- Specifying the wrong quality level for a high-risk corridor is a contractual, financial, and safety liability.
- MAYA Global Group delivers SUE services across all four quality levels, with full compliance to ASCE 38-22.
Why Utility Records Alone Are Not Enough
The instinct to rely on as-built drawings is understandable. They represent what was installed, they are usually available from utility owners or municipal archives, and they carry an implied authority – someone drew them as a record of construction.
The problem is the gap between “drawn” and “accurate today.” As-built records are produced at the time of installation, and from that moment forward they begin to drift from reality. Pipes settle, shift with soil movement, or are displaced by adjacent excavations. Utility owners make emergency repairs that are never formally recorded. Illegal or undocumented connections are made. Abandon-in-place decisions leave assets in the ground that do not appear on any current drawing because they were removed from the active network, not from the physical ground.
Studies consistently find that a significant percentage of utility positions shown on as-built drawings – some analyses put the figure at 30 to 50 percent – are outside acceptable horizontal tolerances, and virtually none of the drawings carry reliable depth information at all.[3] Depth, as explored below under Quality Level A, is the variable that as-built drawings almost never reliably capture even when the horizontal position is correct.
โ ๏ธ Safety Alert
The Common Ground Alliance (CGA) DIRT (Damage Information Reporting Tool) Report tracks utility excavation damage annually. The data consistently shows that a large proportion of utility strikes occur on projects where a locate request was made and records were available – the strike happened because the available information was incomplete or misapplied, not because no information existed. The presence of utility records does not, by itself, constitute adequate risk mitigation.
This is the core problem that ASCE 38 addresses. The standard does not tell you how to find utilities – it tells you how to classify, communicate, and contractually document what level of certainty your utility data represents. A project that specifies Quality Level D utility data is making a documented, defensible statement: “We have reviewed available records. We have not confirmed anything in the field.” That is very different from a project that simply says “we have utility drawings.”
Our underground infrastructure surveys combine record research with field verification to ensure that the data underpinning your project decisions reflects actual ground conditions, not just archived drawings.
Quality Level D: Record Research and Desk Study
Quality Level D is the entry point of the ASCE 38 framework. It involves the collection, review, and synthesis of existing utility records from all relevant sources: utility owners, municipal archives, government agencies, one-call center records, aerial imagery, and any other documentary source that can shed light on what is likely to be in the ground.
The output of a Quality Level D investigation is a compiled utility base map showing all utilities identified through records, typically plotted in plan view with horizontal positions derived from the documents themselves. No field work is performed to verify these positions. No geophysical investigation is conducted. The map reflects what the records say, with accuracy limited by the accuracy of those records.
What Quality Level D Confirms
- The existence of utilities based on documentary evidence
- Approximate horizontal positions as shown in available records
- Utility type, material, and ownership where recorded
- Any conflicts apparent from overlaying records on project plans
What Quality Level D Does Not Confirm
- That the horizontal positions shown are accurate in the field
- That all utilities in the project corridor are represented
- Any depth information
- Current operating status or condition
When Quality Level D Is Appropriate
Quality Level D is appropriate as the initial phase of every SUE investigation – it establishes the documentary baseline that guides all subsequent field work. It may also be sufficient as a standalone deliverable for very early-stage planning, feasibility assessments, or corridor screening where decisions are being made at a regional or network level and no excavation or detailed design work is contemplated.
Using Quality Level D data as the sole basis for excavation planning or trenchless design is not appropriate and represents a significant unquantified risk. The ASCE 38-22 standard is explicit that Quality Level D data must not be relied upon to characterize utility positions for construction purposes.
๐ MAYA Global Insight
In practice, the records collected during a Quality Level D investigation frequently reveal conflicts, gaps, and inconsistencies that would never have been visible from a single utility owner’s drawing alone. MAYA Global Group’s record research protocols include cross-referencing multiple archive sources, historical aerial photography, and permit records – an approach that significantly improves the completeness of the documentary baseline before any field work begins.
Quality Level C: Surface Geophysical Investigation
Quality Level C adds field work to the record-based foundation established by Quality Level D. Specifically, it involves the application of surface geophysical methods to detect and horizontally trace subsurface utilities without excavation.
The geophysical methods applied at Quality Level C vary based on utility type, ground conditions, and the specific objectives of the investigation. Ground Penetrating Radar (GPR) is commonly used to detect both metallic and non-metallic utilities, concrete structures, and voids in the subsurface. Electromagnetic induction (EM) methods are effective for tracing conductive utilities such as metallic pipes and cables. Radio frequency (RF) detection techniques are used where signal transmission or induction on known utilities can assist in tracing their path. In complex environments, multiple methods may be deployed in combination. For a detailed breakdown of how modern radar technology compares to conventional electromagnetic locating in practice, see our guide on GPR HDR vs traditional detection methods.
What Quality Level C Confirms
- Horizontal position of detected utilities, with accuracy limited by the resolution of the geophysical method and operator interpretation
- The presence of utilities not appearing in any records (unrecorded or abandoned assets)
- Approximate horizontal alignment and routing through the project corridor
What Quality Level C Does Not Confirm
- Depth to the top or centerline of any utility
- Utility condition or internal characteristics
- The identity of detected anomalies where geophysical response alone is ambiguous
- Completeness – some utilities (particularly old clay pipes, certain plastics, and utilities below the resolution limit of the equipment) may not be detected
It is important to understand that geophysical methods at Quality Level C provide depth estimates only as a secondary output with significant uncertainty. The horizontal trace is the reliable product. Any depth indication from surface geophysics is an inference, not a measurement, and should not be treated as equivalent to Quality Level A depth data.
When Quality Level C Is Appropriate
Quality Level C is appropriate where a complete picture of utility routing is needed for route selection, conflict screening, or preliminary design – particularly where the record base is known to be incomplete or where unrecorded utilities are expected. It is also used to prioritize which locations require Quality Level A vacuum excavation by identifying the areas of greatest conflict density or uncertainty.
Our GPR HDR subsurface mapping services deliver Quality Level C data using calibrated, multi-frequency ground penetrating radar, producing georeferenced utility trace data that integrates directly into project design environments.
Quality Level B: Designating – Horizontal Position Confirmed
Quality Level B is what most engineers and project managers are referring to when they speak of a “utility locate.” It represents the standard of utility information that one-call or 811 systems in North America are designed to provide, and it is the baseline expectation for excavation work in most jurisdictions with mandatory locate-before-you-dig requirements.
At Quality Level B, a trained technician uses geophysical equipment – typically electromagnetic equipment and/or GPR – to trace utilities in the field and physically mark their horizontal position on the ground surface. These marks are placed using paint, flags, or stakes following the APWA (American Public Works Association) Uniform Color Code, which assigns standard colors to utility types: red for electric, yellow for gas/oil, orange for communications, blue for potable water, green for sewer/drain, purple for reclaimed water, and white for proposed excavation limits.
What Quality Level B Confirms
- Horizontal position of utilities, confirmed in the field by a trained locator using geophysical equipment
- A horizontal accuracy that, under ASCE 38-22, is expected to be within approximately 0.6 meters (2 feet) of actual position for most utility types
- Utility type and ownership attribution based on the locate request and records provided by the utility owner
What Quality Level B Does Not Confirm
- Depth – this is the critical limitation of Quality Level B data
- Utility condition, diameter, or material where not documented in owner records
- Service laterals, stub-outs, or connections not included in the main-line locate
- Detection of non-conductive utilities where no signal path exists (though GPR can assist)
โ ๏ธ Safety Alert
A critical misunderstanding on construction sites is treating Quality Level B marks as a proxy for safe dig depth. They are not. A utility marked on the surface at Quality Level B may be 0.3 meters deep or 3 meters deep. The mark tells you where to look horizontally; it tells you nothing about when your excavation equipment will reach the utility. Proceeding with mechanical excavation to any depth based solely on QL-B data, without Quality Level A depth confirmation at conflict points, is a recognized risk factor in utility strike incidents.
When Quality Level B Is Appropriate
Quality Level B is the appropriate minimum standard for any project involving ground disturbance. It is sufficient for many excavation activities where experienced hand-digging methods are used within the tolerance zone of identified utilities. For deeper excavations, trenchless operations, or situations where utilities are densely clustered, Quality Level B should be followed by Quality Level A investigation at conflict locations.
Quality Level A: Locating – Depth and Condition by Vacuum Excavation
Quality Level A is the highest level of certainty defined in the ASCE 38 framework. It is the only quality level that provides confirmed depth information. At Quality Level A, the actual position of a utility in three dimensions – horizontal x, horizontal y, and vertical depth – is physically measured by exposing the utility using vacuum excavation (also called hydro-excavation or soft-dig) and recording its precise position using survey-grade instruments.
The process involves excavating a controlled test hole (termed a “daylighting” hole or exploratory excavation) using high-pressure water or air combined with vacuum suction to remove the spoil material. This non-destructive method loosens and removes soil around the utility without the mechanical force that a conventional excavator bucket would apply, dramatically reducing the risk of damage to the asset being exposed. Once the utility is visible, the following are recorded:
- Three-dimensional position (x, y, z) measured by survey
- Utility type, material, and nominal diameter
- Condition observations visible at the exposed point
- Coating or lining condition where observable
- Presence of any adjacent utilities not previously identified
The test hole is then carefully backfilled and the surface restored. The data is incorporated into the project base map with a surveyed accuracy typically within 15 mm horizontally and vertically.
What Quality Level A Confirms
- Three-dimensional position at the point of excavation, with survey-grade accuracy
- Depth to top-of-utility and centerline depth
- Physical characteristics (material, diameter, coating) observed directly
- Presence and approximate position of any proximate utilities discovered during exposure
What Quality Level A Does Not Confirm
- Utility position between test hole locations – the data applies at the point of excavation
- Condition of the full utility run beyond what is visible in the test hole
- Operating pressure, flow status, or internal condition
When Quality Level A Is Required
Quality Level A is required wherever the depth of a utility is a design or construction parameter that cannot be left uncertain. Specific scenarios where it should be specified include:
- Trenchless construction crossings – horizontal directional drilling (HDD), pipe jacking, microtunneling, and auger boring require the borehole design to pass at a known clearance from existing utilities. Without QL-A depth data at the crossing point, the safe clearance cannot be confirmed and the bore profile cannot be accurately designed. See our detailed guidance on pre-bore utility clearance protocols for HDD and trenchless projects.
- Deep excavation in congested corridors – where multiple utilities at varying depths must be managed simultaneously and mechanical excavation will approach the utilities. Projects involving pile installation and basement construction in mature urban grids should also refer to our guidance on deep foundation utility clearance.
- Conflict resolution – where a proposed pipe or duct must cross an existing utility and the required vertical clearance must be confirmed by measurement rather than estimated from records.
- High-consequence utilities – gas transmission mains, high-voltage electric cables, and telecom fiber with critical service obligations warrant Quality Level A confirmation wherever excavation approaches.
- Renovation and retrofit projects – where records are decades old and the installation methods used at the time (manual excavation, no GPS) produce particularly unreliable depth information.
โ Best Practice
On trenchless projects, specify Quality Level A test holes at each utility crossing plus at least one intermediate point per 30-50 meters of bore path in areas of high utility density. This spacing gives the design engineer the vertical profile data needed to confirm clearance and adjust the bore trajectory if needed – before the boring equipment is on site. The cost of additional test holes during design is a small fraction of the cost of a utility strike during boring operations.
Cost vs. Value of Quality Level A
Quality Level A is the most expensive SUE quality level, primarily because it involves vacuum excavation equipment, survey crews, and traffic management at each test hole location. On large projects with many required test holes, the cost can be significant in absolute terms.
The cost-benefit analysis is straightforward, however. A single utility strike during construction typically costs an order of magnitude more than the full SUE program that would have prevented it – when downtime, repairs, third-party liability, project delay, and regulatory penalties are aggregated. Studies examining infrastructure project budgets consistently find that SUE programs – including Quality Level A investigation – produce positive returns on investment across the range of project types and sizes examined.[3]
Our non-destructive utility mapping services include vacuum excavation and survey-grade test hole recording, delivering Quality Level A data that integrates directly into project design and BIM environments.
Choosing the Right Quality Level for Your Project Type
The ASCE 38-22 standard does not prescribe a single quality level for all projects. It provides a framework within which engineers and project owners make risk-informed decisions about what level of certainty is required given the specific nature of the work, the consequences of a utility strike, and the utility density of the project corridor. The following matrix summarizes appropriate quality level selection by project type.
| Project Type | Minimum Recommended QL | QL-A Trigger Conditions |
|---|---|---|
| Early-stage planning / feasibility | D | Not typically required at this stage |
| Route selection / corridor screening | C or B | High-consequence utility crossings identified in QL-C/B phase |
| Shallow open-cut excavation (<1.2m) | B | Dense utility corridor, high-pressure or high-voltage assets nearby |
| Deep open-cut excavation (>1.2m) | B + A at conflicts | All depth-critical conflict points; high-consequence assets |
| Trenchless installation (HDD, microtunnel) | A at all crossings | Required at every utility crossing plus intermediate bore path points |
| Building foundation / basement excavation | B + A at perimeter | Service connections entering the building footprint |
| Infrastructure renovation in aged network | C + B + A | All depth-critical points; records assumed unreliable for depth |
| Road widening / pavement rehabilitation | B | Subgrade treatment approaching service lateral depth |
The matrix above reflects general guidance. The specific geology, utility ownership complexity, regulatory environment, and contractual risk allocation on any project will influence the appropriate quality level specification. A formal SUE risk assessment conducted during the design phase is the most defensible basis for quality level selection decisions. For projects where proposed utilities must be routed through congested existing networks, integrating subsurface clash detection workflows into the design process provides an additional layer of spatial conflict analysis before ground disturbance begins.
๐ MAYA Global Insight
One of the most common errors in quality level specification is applying a blanket quality level to an entire project corridor when a risk-differentiated approach would be both more protective and more cost-effective. MAYA Global Group routinely assists project teams in developing quality level allocation plans that apply QL-A selectively to the highest-risk conflict points while using QL-B as the standard across lower-risk corridor segments – achieving better risk coverage at a lower total program cost than a uniform QL-A specification would produce.
ASCE 38-22: What Changed from the 2002 Standard
The original ASCE 38 standard was published in 2002 as ASCE 38-02, titled “Standard Guideline for the Collection and Depiction of Existing Subsurface Utility Data.” It established the four quality levels (D through A) and the fundamental framework for SUE data classification that the industry has used for over two decades.
The 2022 revision – ASCE 38-22 – updated and expanded the standard in several significant ways that practitioners need to understand:[2]
Key Changes in ASCE 38-22
Updated title and scope. The 2022 edition is formally titled “Standard Guideline for Investigating and Documenting Existing Utilities.” The revised title reflects a broader scope that encompasses not just data collection and depiction but the full investigative process, including field methods and documentation requirements.
Expanded Quality Level B definition. The 2022 edition clarifies and expands the requirements for Quality Level B designating, including explicit requirements for the documentation of geophysical methods used, equipment calibration records, and operator qualifications. The standard moves toward greater accountability for the reliability of field-confirmed horizontal data.
Quality Level A test hole documentation. ASCE 38-22 introduces more specific requirements for test hole data recording, including required data fields for utility material, size, condition observations, and the survey method used to establish position. This standardization makes Quality Level A data more consistent and more readily usable by design engineers from different project teams.
Integration with BIM and GIS environments. The 2022 standard acknowledges the widespread adoption of Building Information Modeling (BIM) and Geographic Information System (GIS) platforms and provides guidance on how SUE data at each quality level should be attributed and symbolized in these environments.
Risk-based quality level selection guidance. The revised standard strengthens the guidance on how to select quality levels based on project risk, moving toward a more explicit risk-matrix approach rather than leaving the selection entirely to the engineer’s discretion.
Alignment with CI/ASCE 38. The 2022 edition improves alignment with the ASCE Construction Institute’s broader body of standards for underground construction, creating better interoperability between SUE data standards and construction method standards for trenchless technology and open-cut excavation.
โ Best Practice
Contract specifications for SUE services should explicitly reference ASCE 38-22 (not the 2002 edition) and should specify both the quality levels required and the documentation format expected for deliverables. Vague specifications that require “utility location” without a quality level designation create ambiguity about what the contractor is required to deliver and what the project owner is entitled to rely upon.
The Utility Engineering and Surveying Institute (UESI) of the American Society of Civil Engineers is the technical home for the development and maintenance of ASCE 38 and related standards, and is the authoritative source for updates to the standard as the SUE practice continues to evolve.[2]
Ready to specify the right quality level for your project?
Contact MAYA Global Group for subsurface utility engineering services – Contact Us
Frequently Asked Questions
Glossary of Key Terms
SUE (Subsurface Utility Engineering)
An engineering discipline that applies systematic processes to identify, classify, and communicate information about existing subsurface utilities. SUE integrates record research, surface geophysics, and vacuum excavation to produce utility data at defined quality levels.
Quality Level A (QL-A)
The highest SUE quality level. Utility position is confirmed in three dimensions by vacuum excavation and survey measurement. The only quality level that provides confirmed depth data. Also called “locating.”
Quality Level B (QL-B)
Horizontal position of utilities confirmed in the field by a trained technician using geophysical equipment. Marks are placed on the ground surface. Depth is not confirmed. Also called “designating.”
Quality Level C (QL-C)
Horizontal utility traces obtained by surface geophysical methods (GPR, electromagnetic). Detects utilities not in records. Depth is inferred only – not confirmed. Used for routing and conflict screening.
Quality Level D (QL-D)
Record research and desk study. Utility information compiled from available archives and documentation. No field verification. Represents documentary evidence only – the starting point for all SUE investigations.
Vacuum Excavation
Non-destructive excavation method using high-pressure water or air to loosen soil, with a vacuum system to remove spoil. Used for Quality Level A test holes. Also called hydro-excavation or soft-dig. Minimizes risk of utility damage during exposure.
Designating
The process of using surface geophysical methods to trace and mark the horizontal position of subsurface utilities. Corresponds to Quality Level B in ASCE 38. Does not confirm depth. Marks are typically applied using APWA color-coded paint or flags.
Locating
In the SUE context, locating refers specifically to Quality Level A – the physical exposure and three-dimensional measurement of a utility by vacuum excavation. Distinct from the more general use of “locating” to mean any utility detection activity.
ASCE 38
Standard Guideline for Investigating and Documenting Existing Utilities, published by the American Society of Civil Engineers. Current edition is ASCE 38-22 (2022). The foundational standard for subsurface utility engineering quality levels and data classification in the United States and internationally.
As-Built Drawings
Construction drawings revised after installation to reflect what was actually built, including any field changes. As-built records for underground utilities are commonly inaccurate in horizontal position and rarely include reliable depth information. Form the basis of Quality Level D investigation but require field verification at higher quality levels.
References
- Common Ground Alliance. DIRT Report – Damage Information Reporting Tool Annual Report. Common Ground Alliance, published annually. Available at: commongroundalliance.com
- American Society of Civil Engineers, Utility Engineering and Surveying Institute (UESI). ASCE 38-22: Standard Guideline for Investigating and Documenting Existing Utilities. ASCE, 2022. See also: ASCE Utility Engineering and Surveying Institute
- Anspach, J.H. Cost Savings on Highway Projects Utilizing Subsurface Utility Engineering. Report prepared for the Federal Highway Administration, Transportation Research Record. National Academies of Sciences, Engineering, and Medicine.
